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Full text of "The manufacture and properties of iron and steel"

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70                            METALLURGY OF IKON AND STEEL.
The Middlesborough and Pittsburg furnaces represent two extremes of good practice; one with lean ores and slow-running, and the other with rich ores and fast-running, and from Tables II-C and II-D the following conclusions may be drawn:
(1)   Of all the heat energy contained in the coke charged in a blast furnace, one-half goes away in the tunnel head gases, part as sensible heat, but most of it as unburned CO.
(2)   The proportion of "heat so lost is about the same whether the furnace is working1 on lean ores with a high consumption of fuel or on rich ores with a low fuel ratio.
(3)-The other half of the energy is used in reducing the iron ore, in melting the iron and slag, in losses from conduction and radiation, and in minor chemical reactions.
(4)   The proportion of the total energy used for each one of these items depends upon the special conditions; as, for instance, the proportion needed for the reduction of C02 and the proportion needed for the melting of the slag both depend on the amount of limestone needed, and this, in turn, depends on the impurities in ore and fuel.    In the reduction of the ore and the fusion of the pig-iron, both of which take a given amount of heat, the proportion which this given amount bears to the total will depend solely upon what the total is, being greater with a small fuel ratio.
(5)   The proportion lost in radiation and through the cooling water will decrease as the output of the furnace is increased, either by the use of rich ores or by rapid driving, or both.
(6)   The reduction of the ore calls for between 20 and 25 per cent, of all the energy delivered to the furnace.
(7)   The fusion of the pig-iron requires from 4 to 5 per cent.
(8)   The fusion of the slag requires from 4.5 to 9.4 per cent., increasing with the amount of impurities and the quantity of stone.
(9)   The heat lost by radiation and in cooling water varies from 4.5 to 6.0 per cent., decreasing with a larger output of pig-iron.
(10)   The reduction of the metalloids, the expulsion of C02 from limestone, and the reduction of this C02 to CO, each requires:'from 2 to 3 per cent.
(11)  The dissociation of CO, and the decomposition of water in the blast, each calls for from 1 to 2 per cent., while the evaporation of the water in the coke takes a small fraction of 1 per cent.
(12)   Some factors are beyond the control of the smelter, as for in-